Such a structure is particularly suited to high-frequency (HF) applications; that is to say, applications above 100 MHz, for example, a radio-frequency (RF) application for integrated circuits with an operating frequency with an order of magnitude of a few GHz, the support substrate being highly resistive (that is to say, that the predetermined resistivity value is greater than 500 Ω·cm).
One fabrication method known from the prior art, notably from French Patent FR 2 953 640 (hereinbelow D1), comprises the steps of: a) providing a donor substrate produced in the semiconductor material, b) forming an embrittlement area in the donor substrate so as to delimit a first portion and a second portion of the donor substrate on either side of the embrittlement area, the first portion being intended to form the active layer, c) providing the support substrate having a resistivity greater than a predetermined value, d) forming the separator layer on the support substrate, e) forming the dielectric layer on the first portion of the donor substrate and/or on the separator layer, f) assembling the donor substrate and the support substrate through the intermediary of the dielectric layer and the separator layer, g) fracturing the donor substrate along the embrittlement area so as to obtain the structure, and h) subjecting the structure to a strengthening annealing of at least 10 minutes after step g).
As specified in D1, the strengthening annealing is executed during step h) at a temperature less than 950° C. so that the heat budget applied is not sufficient to transform the polycrystalline silicon of the separator layer into monocrystalline silicon. It is essential for the separator layer not to be transformed into monocrystalline silicon in order to retain a resistivity of the structure that is satisfactory for RF application.
D1 stresses that the fact that limiting the duration and/or the temperature of the strengthening annealing generates an embrittlement in the interface created during assembly step f). D1 remedies this drawback by intermediate treatments, such as a plasma treatment, capable of strengthening the cohesion of the structure.